1. Field of the Invention
The present invention relates to an electrode tab for a secondary battery and a secondary battery using the same.
2. Description of the Related Art
Secondary batteries are rechargeable batteries using reversible conversion between chemical energy and electrical energy.
As portable electronic appliances such as mobile phones, notebook computers, PDAs and camcorders are further developed, a demand for secondary batteries, especially lithium secondary batteries, is rapidly increasing.
Such lithium secondary batteries include lithium metal secondary batteries, lithium ion secondary batteries, lithium ion polymer secondary batteries and lithium polymer secondary batteries.
Lithium ion secondary batteries having a voltage of 3.6V are widely used because of their high performance and light weight.
Typical lithium ion secondary batteries include an electrode assembly having a positive electrode plate, a negative electrode plate and a separator, and an electrolyte for transferring lithium ions.
Further, lithium ion secondary batteries may include a protection circuit to prevent explosion and inflammation caused by a leakage of the electrolyte or by an increase in internal pressure.
A conventional lithium polymer secondary battery having a voltage of 3.6V has a low possibility of explosion, and may be formed in various shapes by using a gel-type electrolyte.
A conventional lithium polymer secondary battery includes an electrode assembly having a positive electrode plate, a negative electrode plate and a separator interposed between the two electrode plates to serve as an isolation layer and simultaneously as an electrolyte.
Lithium polymer secondary batteries are resistant to a chemical reaction caused by overcharge or overdischarge by using a polymer gel-type electrolyte, and therefore do not need a protection circuit.
Such lithium secondary batteries may be classified into prismatic, cylindrical and pouch types according to the shape of an outer casing accommodating an electrode assembly.
Electrode tabs are attached to positive and negative electrode plates to transmit electrons generated from the electrode assembly accommodated in the outer casing to the exterior.
When an external pressure is applied to the outer casing accommodating the electrode assembly to which the electrode tab is attached, the outer casing and the electrode assembly accommodated therein may be transformed, i.e., bent or distorted.
The electrode tab may also be distorted, depending on its position relative to where the external pressure is applied, or it may maintain its original shape without distortion.
When the electrode assembly is distorted, but the electrode tab is not distorted, the electrode assembly may be damaged by a corner of the electrode tab, and thus an electrical short circuit may occur in the damaged portion.
More specifically, the electrical short circuit may easily occur when the electrode assembly is bent toward the electrode tab at the corner of the electrode tab.
Moreover, the electrical short may easily occur at a long side of the electrode tab, rather than a short side thereof.